Flying King Rido went back to the past through his "relentless efforts", stole the fragments of Crowrid's soul at the moment of his death, and created a "replica" that possessed Crowrid's magic power and looked almost the same as him. He wanted to use him to interfere with the witch and not let her disturb him from realizing his wish.
However, things don't always go so smoothly.
The encounter between the replica and the witch is inevitable, so perhaps his encounter with Chrollo is also inevitable.